1. Filed of the Invention
This invention relates generally to the completion of junctions between primary and lateral wellbores. More particularly, this invention relates to new and improved methods and devices for sealing the junction of a branch wellbore extending laterally from a primary well which may be vertical, substantially vertical, inclined or even horizontal. This invention finds particular utility in the sealing of junctions of multilateral wells, that is, downhole well environments where a plurality of discrete, spaced lateral wells extend from a common primary wellbore.
2. Prior Art
Lateral well drilling and production have been increasingly important to the oil industry in recent years. While lateral wells have been known for many years, only relatively recently have such wells been determined to be a cost effective alternative (or at least companion) to conventional well drilling. Although drilling a lateral well costs substantially more than its vertical alternative, a lateral well frequently improves well productivity by several fold. Lateral drilling provides the means for enhancing field economics by accessing and developing reservoirs that would otherwise be uneconomic to develop using conventional drilling and completion practices. Hydrocarbon reservoirs that are ideal candidates for lateral technology are those that are thin and limited in size, multi faulted, or naturally fractured. Other reasons for employing laterals are to address reservoir vertical conformance, oil and gas coning potential and sweep efficiency. Environmental issues, such as the number of drilling sites in sensitive areas can also be addressed with lateral technology. In addition, improved field development economics can be achieved in large reservoirs using multiple laterals by improving the productivity of individual wells thereby reducing investment and operational costs.
Some wells contain additional wellbores extending laterally from the lateral. These additional lateral wells are sometimes referred to as drain holes and primary wells containing more than one lateral well are referred to as multilateral wells. Multilateral wells are becoming increasingly important, both from the standpoint of new drilling operations and from the increasingly important standpoint of reworking existing wellbores including remedial and stimulation work.
As a result of the foregoing increased dependence on and importance of lateral wells, lateral well completion, and particularly multilateral well completion have posed important concerns and have provided (and continue to provide) a host of difficult problems to overcome. Lateral completion, particularly at the juncture between the primary and lateral wellbore is extremely important in order to avoid collapse of the well in unconsolidated or poorly consolidated formations. Thus, open hole completions are limited to competent rock formations; and even then, open hole completions are inadequate in many cases since there is limited control or ability to re-access (or re-enter) the lateral or to isolate production zones within the well. Coupled with this need to complete lateral wells is the growing desire to maintain the size of the wellbore in the lateral well as close as possible to the size of the primary wellbore for ease of drilling and completion.
Conventionally, lateral wells have been completed using either slotted liner completion, external casing packers (ECP's) or cementing techniques. The primary purpose of inserting a slotted liner in a lateral well is to guard against hole collapse. Additionally, a liner provides a convenient path to insert various tools such as coiled tubing in a lateral well. Three types of liners have been used: (1) perforated liners, where holes are drilled in the liner, (2) slotted liners, where slots of various width and depth are milled or wire wrapped along the liner length, and (3) prepacked liners.
Slotted liners provide limited sand control through selection of hole sizes and slot width sizes. However, these liners are susceptible to plugging. In unconsolidated formations, wire wrapped slotted liners have been used to control sand production. Gravel packing may also be used for sand control in a lateral well. The main disadvantage of a slotted liner is that effective well stimulation can be difficult because of the open annular space between the liner and the well. Similarly, selective production (e.g., zone isolation) is difficult.
Another option is a liner with partial isolations. External casing packers (ECPs) have been installed outside the slotted liner to divide a long lateral well bore into several small sections. This method provides limited zone isolation, which can be used for stimulation or production control along the well length. However, ECP's are also associated with certain drawbacks and deficiencies. For example, normal lateral wells have many bends and curves. In a hole with several bends it may be difficult to insert a liner with several external casing packers.
Finally, it is possible to cement and perforate medium and long radius wells, as shown, for example, in U.S. Pat. No. 4,436,165.
The problem of lateral wellbore (and particularly multilateral wellbore) completion has been recognized for many years as reflected in the patent literature. For example, U.S. Pat. No. 4,807,704 discloses a system for completing multiple lateral wellbores using a dual packer and a deflective guide member. U.S. Pat. No. 2,797,893 discloses a method for completing lateral wells using a flexible liner and deflecting tool. U.S. Pat. No. 2,397,070 similarly describes lateral wellbore completion using flexible casing together with a closure shield for closing off the lateral. In U.S. Pat. No. 2,858,107, a removable whipstock assembly provides a means for locating (e.g., re-entry) a lateral subsequent to completion thereof. U.S. Pat. No. 3,330,349 discloses a mandrel for guiding and completing multiple lateral wells. U.S. Pat. No. 5,318,122, which is assigned to the assignee hereof and incorporated herein by reference, discloses deformable devices that selectively seal the juncture between the primary and lateral wells using an inflatable mold which utilizes a hardenable liquid to form a seal, expandable memory metal devices or other devices for plastically deforming a sealing material. U.S. Pat. Nos. 4,396,075; 4,415,205; 4,444,276 and 4,573,541 all relate generally to methods and devices for multilateral completion using a template or tube guide head. Other patents and patent applications of general interest in the field of lateral well completion include U.S. Pat. Nos. 2,452,920, 4,402,551, 5,289,876, 5,301,760, 5,337,808, Australian patent application 40168/93, U.S. application Ser. No. 08/306,497 filed Sep. 15, 1994, now U.S. Pat. No. 5,526,880, which is assigned to the assignee hereof and incorporated herein by reference, and U.S. Ser. No. 08/188,998 filed Jan. 26, 1994, now U.S. Pat. No. 5,474,131, which is also commonly assigned and incorporated herein by reference.
Notwithstanding the above-described attempts at obtaining cost effective and workable lateral well completions, there continues to be a need for new and improved methods and devices for providing such completions, particularly sealing between the juncture of primary and lateral wells, the ability to re-enter lateral wells particularly in multilateral systems) and achieving zone isolation between respective lateral wells in a multilateral well system.
Some of the most recent developments include the following: one method for cementing the junction between the main borehole and the lateral borehole addresses the issue of creating a window in the main (or primary) hole, drilling a lateral wellbore and then sealing the juncture between the lateral and primary wellbores to have the ability to re-enter each lateral wellbore as well as to maintain the option to perform any function that could be done in a single wellbore. For this reason, cemented lateral wellbores are desirable so that normal isolation, stimulation or any other operation can be achieved.
In accordance with this prior art method, prior to running in a novel "hook" liner system described hereinafter, a standard whipstock is used to mill out a window in the side of the casing of the primary wellbore at the location where it is desired to drill a lateral wellbore.
In accordance with this prior art method, prior to running in a hook hanger system (fully described in U.S. Pat. No. 5,477,925, and briefly described hereinafter) a standard whipstock is used to mill a window in the side of the casing of the primary wellbore at the location where it is desired to drill a lateral wellbore.
The hook liner hanger is run on top of the lateral liner. The liner is run into the main casing and then out through the aforementioned milled window. The hook liner hanger has a pre-machined window, a hook system, and a re-entry system. When the hook on the hanger locates on the main casing milled window, it orients the hanger, so that the pre-machined window is aligned with the lower part of the main casing below the milled window. The running system for the hook liner hanger, includes a method of isolating the pre-machined window from the bore of the hook liner hanger. If desired the liner can be cemented in place, using standard cementing techniques commonly used in regular liner placements. The hook liner hanger can be run in various combinations to suit the needs of the wellbore. These combinations can include equipment such as external casing packers, sand control screens, partially cemented liner, fully cemented liner, and liner hanger packers.
When the hook hanger is to be cemented in place, a tube is attached to the lower end of the liner hanger running tool that extends below the pre-machined window. The annular space between the tube and the Liner Hanger body is sealed, so that the cement does not circulate back through the pre-machined window. After the cement has been pumped in place, the tube can be pulled back above the pre-machined window and then diverted back down through the pre-machined window to clean out the flow path back to the main casing below the milled window.
A variation of the hook liner hanger is a version where the formation can be hydraulically sealed from the lateral liner, the lower main casing and the upper main casing. A short section of casing extends from the periphery of the pre-machined window in the hook liner hanger. The end of this section is cut obliquely so that when being run it is possible to run inside the main wellbore casing, yet when landed will still extend from the hook liner hanger. After the hook liner hanger is fully positioned and any cementing has taken place, a tie back assembly is employed which will go through the pre-machined window in the hook liner hanger and land in the packer positioned below the window which was initially positioned for the whipstock. When the anchor lands in the packer it will orient in the same manner as the whipstock did. The orientation will also align a seal system which will land in the short section of casing extending from the hook liner hanger. The seal system can be of any of the common types such as a packing element, chevron seal system, or an interference seal system.
The "hook" liner hanger system includes a "hook" and is run into the wellbore and then through the aforementioned milled window. The "hook" liner hanger system is run into the lateral wellbore until the "hook" hanger locates on the milled window in the main primary wellbore. Inside the "hook" liner hanger system is a tail pipe assembly with adjustable opposing swab cups. The tail pipe assembly carries liquid cement or other fluids as required to inflate external casing packers or other devices as required. The end of the "hook" hanger liner is then plugged to allow the hydraulic set hanger to set by means of applied pressure. An external casing packer located near the end of the "hook" liner hanger system is then inflated to seal the lateral wellbore annular space just below the cementing valve of the "hook" liner hanger system. Opposing "swab-cups" are used to direct fluid to inflate the external casing packer.
The tailpipe assembly string is then withdrawn high enough to allow the end of the tailpipe assembly string to be pulled from the lateral wellbore and then lowered into the main wellbore through the premilled window of the "hook" liner hanger system to assist in reducing debris from falling into the main wellbore. While the system does create a good sealed junction it is a difficult process and an easier and more speedy process is always desirable.
U.S. Pat. No. 5,318,122 discloses a number of embodiments employing differing forms and hardenable filling materials. The methods include employing 1) an inflatable mold which utilizes a hardenable liquid like epoxy or cement; 2) expandable memory metal devices; 3) swaging devices for plastically deforming a sealing material; 4) liner seals for sealing between the liner and the primary bore; and 5) side pocket devices to guide a liner into the lateral.
All of the prior art devices and methods while performing well for their intended functions are still in need of improvement. A particular area of improvement desired is in the cement at the junction which in present art is employed as both the junction and the seal. This works marginally well and is subject to failure due to limitations in the cement material itself or the ability to place the cement successfully at the junction. More particularly, under the conditions downhole, cement can fail by deteriorating to such an extent that the seal begins to leak thus contaminating the production. Therefore it is desirable to provide alternate junction creating and sealing arrangements which may be more reliable and improved performance under downhole conditions.